Database Triggers

The difference between Before and After Triggers in MySQL

FREE TRIAL brilliant web hosting in the US.

FREE TRIAL brilliant web hosting in the UK.

What is the difference between before and after triggers in MySQL.

The biggest difference between the before and after trigger in MySQL is that before the before trigger starts, there is an action before a certain operation is performed on the table, while the after trigger performs an action after a certain operation on the table has been executed.

MySQL is a popular database management system that allows users to easily retrieve and manage data in relational databases. It stores data in a tabular form. The user can perform various operations on data using Structured Query Language (SQL). While, Trigger is a store program that runs automatically when an event occurs. The response to the trigger depends on the trigger type.

Key Areas Covered

1. What is Trigger in MySQL
– Definition, functionality
2. What is the before Trigger in MySQL
– Definition, functionality < br />

3. What is after Trigger in MySQL
– Definition, functionality
4. What is the difference between Before and After Trigger in MySQL
– Comparison of the most important differences

 

What is a trigger in MySQL

A trigger is a series of actions that respond to an operation such as inserting, updating, or deleting an operation in a specific table . The trigger is activated when an SQL operation is performed. In addition, it is possible to create triggers with referential constraints and to control constraints that allow the application of data integrity rules. In addition, trigger helps to update other tables. It also automatically generates or converts values ​​for inserted or updated records or performs tasks such as sending alerts.

What is the before Trigger in MySQL

The before trigger is a trigger that is performed before an operation such as insert, update, delete. The user can write these triggers in several cases. They help to check or change values ​​before data is updated or inserted in the database. It is also possible to perform other non-database operations that are encrypted in user-defined functions.

An example of a trigger before the insertion operation is performed.

CREATE TRIGGER TRIGGER_NAME

BEFORE INSERTING

ON table name FOR EACH ROW

START

– variable returns

– trigger code

END;

The trigger_name is used to identify the trigger. It is the name of the trigger to create. The “INSIDE INSERT” statement indicates that the trigger is activated before the insertion operation is performed. The table name indicates the name of the table on which the trigger was created. These triggers will update the new values. Old values ​​in the table remain the same.

What is After Trigger in MySQL

After trigger is a trigger that is executed after an operation such as insert, update, delete. The user can write these triggers in several cases. He can use them to update data in tables. He can also use it to perform non-database operations that are encoded in user-defined functions.

An example of a post-insertion trigger is as follows.

CREATE TRIGGER < em> TRIGGER_NAME

AFTER INSERT

ON table name FOR EVERY ROW

START

– variable declarations

– trigger code

END;

The trigger_name is used to identify the trigger. It is the name of the trigger to create. The “AFTER INSERT” instruction indicates that the trigger is triggered after the insert operation. The table name indicates the name of the table on which the trigger was created. These triggers will update the new values. Old values ​​remain the same.

Difference between the two triggers

Before Trigger is a trigger type that is automatically executed before a certain operation on the table takes place. In contrast, after trigger is a type of trigger that is executed automatically after a certain operation has taken place on the table. Hence, these definitions explain the fundamental difference between before and after trigger in MySQL.

Use

Typically, the use of Before triggers is to perform validation before data is accepted in the table and to check the values ​​before they are removed from the table. However, the use of After triggers is usually to update data in a table due to a change that has occurred. Therefore, the main difference between before and after trigger in MySQL is where we use them.

Example

In a banking application, it helps to check the values ​​before the trigger is deleted before it is deleted, while the after trigger helps to update the balance in the table of accounts.

Conclusion

The main difference between before and after trigger in MySQL is that the Before trigger performs an action before a certain operation is performed on the table, while the After trigger performs an action after a certain operation is performed on the table.

Reference:

1. “Types of Triggers”, ORACLE DOCS.

Leave a Comment